The present invention relates to injection molded thermoplastic closures for bottles and like containers and, in particular, to such closures with improved sealing capabilities.
U.S. Pat. Nos. 4,693,399, 4,936,494, 5,048,730 and 5,330,082 disclose flap type screw-on dispensing closures. In particular, U.S. Pat. No. 5,048,730 discloses a type of cap that has features to improve moisture resistance. Dispensing caps, particularly those combined with a package for liquids are often used with a separate liner that forms a one-time seal onto the mouth of a bottle. Typically, such seals are of the induction type well known in the art. As far as is known, there has been an unfulfilled need for a dispensing closure that has a capability of resealing the bottle mouth with an effectiveness sufficient to be drip resistant and/or highly moisture resistant. Among the problems encountered in making a suitable closure is that the resealability should be achieved at relatively low application torque so that the closure can be used by a person with low hand strength, low finger dexterity and/or with a low attention level. Induction sealed liners are frequently used in the packaging industry because of the performance that can be achieved with this liner. The problem that this type of liner introduces is that the heat generated during the induction process can adversely affect the sealing surface of the cap. Where the sealing surface is originally relatively flat, a good induction seal can be achieved, but the resealability of the cap can be defeated where the heat causes the cap sealing surface to permanently deform and conform to the irregularities in the mouth of the bottle. Thin annular formations in the sealing area of the cap such as shown in the aforementioned U.S. Pat. No. 5,048,730 can also be damaged by the heat of the induction sealing process.
In addition to the difficulty in providing resealability with the mouth of a bottle, there are problems with sealing the flap of a flap-type closure. These problems are exacerbated where the closures are produced in large multi-cavity molds for reasons of economy. It is difficult to maintain accuracy between the two halves of a large multicavity mold because the mold halves can thermally expand at different rates during a production run.